The present invention relates to a microwave oven. More specifically, the present invention relates to a microwave oven that automatically ends a heating operation by detecting the temperature of the food in the heating chamber.
In a conventional microwave oven described in Japanese patent number 2,998,607, detection of the temperature of the food in the heating temperature is performed continuously. Heating is stopped automatically when the food reaches a predetermined temperature. More specifically, when the maximum temperature of the food in the heating chamber reaches a predetermined temperature, i.e., when the difference between the maximum temperature and the minimum temperature of the detection outputs at multiple positions in the heating chamber are at or greater than a predetermined value, the heating is determined to be finished and the heating operation is stopped.
However, in some cases food may be arranged over a relatively wide area in the heating chamber, e.g., when multiple pieces of food are placed in the heating chamber. In these cases, stopping the heating operation as described above for conventional microwave ovens can result in some oft food not being completely heated. This occurs because some of the food may not be completely heated in some locations even when the heating operation is finished for one or more other position inter heating chamber. Also, even for similar foods, the degree of heating that takes place may vary according to the arrangement of the food. This problem is compounded when foods of different types are loaded into the heating chamber.
It is an object of the present invention to provide a microwave oven which overcomes the problems of the prior art.
It is a further object of the invention to provide a microwave oven that can determine an appropriate time to stop heating even when food is arranged at multiple locations within the heating chamber.
It is a still further object of the invention to provide a microwave oven that can determine an appropriate time to stop heating based on a detected lowest food temperature in the heating chamber.
According to one aspect of the present invention, a microwave oven includes: a heating chamber holding food; a magnetron oscillating microwaves to heat the food; a temperature detector detecting temperatures at a plurality of locations in the heating chamber; a controller controlling heating operation of the magnetron based on detection output from the temperature detector. The controller includes: a first evaluation module evaluating whether a maximum temperature in the heating chamber detected by the temperature detector has reached a predetermined value when the magnetron is performing the heating operation; a second evaluation module which, if the first evaluation module determines that the maximum temperature in the heating chamber has reached the predetermined temperature, determines whether there is a particular position, other than the position that reached the predetermined temperature, in the heating chamber that has not reached at least a predetermined temperature lower than the predetermined temperature; a heating operation stopping module which, if the second evaluation module determines that there is the particular position, stops the heating operation of the magnetron when a temperature of the particular position reaches the predetermined temperature.
As a result, if multiple food items are disposed in the heating chamber, heating operations are continued until all the food is sufficiently heated rather than just one food item.
Thus, an appropriate time to end heating is determined even with multiple food items placed in the microwave oven at the same time.
In the microwave oven of the present invention, it is preferable to further include a main unit storage module storing information, disposed separately from the temperature detector. The temperature detector includes an infrared sensor and a correction information storage module storing information used to correct the detected temperature from the infrared sensor. The controller stores storage contents of the correction information storage module in the main unit storage module when a first operation is performed.
As a result, in this microwave oven, the controller stores the storage contents of the correction information storage module in the main unit storage module the first time the microwave oven is operated. This allows the infrared sensor to operate regardless oft durability of the correction information storage module.
This allows the use of low durability in the correction information storage module and thus reduces the cost of the correction information storage module. As a result, the cost of the microwave oven is reduced.
In the microwave oven of the present invention, it is preferable to further include a temperature detection controller controlling the temperature detector to repeatedly change the position at which temperature detection is performed using a predetermined pattern. While the magnetron is performing heating operations, operation of other elements associated with the heating operation are synchronized by the controller with a start of execution by the temperature detection controller of temperature detection according to the predetermined pattern.
As a result, the temperature detector detects temperatures under the same condition each time the predetermined pattern is executed.
In the microwave oven of the present invention, it is preferable for the controller to further include a placement position determining module which, when a temperature detected by the temperature detector is outside a certain range, determines a food placement position, i.e., a position at which the temperature was detected. If the temperature at the food placement position is lower than a predetermined temperature below a normal temperature, the temperature detection controller keeps the position at which the temperature detector module detects the temperature at the food placement position while the magnetron is performing heating operations.
As a result, even if the food has a low temperature, it is possible to avoid the detected food temperature being influenced by higher surrounding temperatures.
In the microwave oven of the present invention, it is preferable for the temperature detector to apply correction to temperatures at a plurality of positions in the heating chamber based on a temperature at a position in the heating chamber which does not contain food when the magnetron begins heating operations. This procedure relies on the fact that, in the absence food at a particular location in the oven chamber, the non-food target area, is not heated substantially by microwave energy. Thus, the correction temperature provides a baseline temperature.
In the microwave oven of the present invention, it is preferable for the temperature detector to detect temperatures at a plurality of positions in the heating chamber using as a reference the temperature detected at a start of the heating operation oft magnetron from a position in the heating chamber at which food is absent.
As a result, in this microwave oven, the environmental temperature of the heating chamber at the start of the heating operation is reflected in the detection output of the temperature detector.
Thus, the detection output of the temperature detector is based on the state of the microwave oven when the heating operation was started. In other words, the precision of the detection output is not affected by the internal temperature of the microwave oven at the start of the heating operation.
In the microwave oven of the present invention, it is preferable to have the following: when the heating operation by the magnetron is started, the controller disables the detection output of the temperature detector for a location at which the temperature detector detects a temperature of at least a predetermined value.
As a result, in the microwave oven, if a section of the heating chamber has a high temperature at the start of a heating operation even in the absence of food in that location, the microwave oven is prevented from mistakenly assuming that sufficiently heated food is located at that section.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.